This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Yerkes National Primate Research Center (YNPRC) has been noted to have a relatively high case load of retained placentas post-partum in the rhesus macaque breeding colony. The standard treatment for this post-partum complication at YNPRC is repeated injections of oxytocin to stimulate uterine contraction along with dilation and curettage (D&C) to loosen and remove remaining placental tissue. This procedure is not always immediately efficacious and can result in incomplete removal of the entire placenta and thus increased likelihood of infection and an increased length of hospitalization. Recent studies in human medicine have shown that either intravenous (50-500 micrograms) or sublingual (1mg) nitroglycerin is effective in inducing uterine relaxation within 60-90 seconds which facilitates removal of the retained placenta. There is currently only one case report involving a retained placenta in a non-human primate (Golden Lion tamarin). The goal of this project is to document the incidence of retained placenta cases in a breeding colony of rhesus macaques, identify any potential etiologies or predisposing factors, and test the usefulness or success of nitroglycerin in facilitating removal of retained placentas in this species. During the breeding season of 2009 there were approximately six cases of retained placentas that were treated with the experimental nitroglycerin protocol. These cases will be compared with historical controls of which approximately 40 cases have been retrospectively reviewed. Serum oxytocin levels have been collected from 10 normal post partum females and 12 retained placenta cases. Initial analysis of this data reveals a significant difference between oxytocin levels of normal females and retained placenta cases. The preliminary data has been presented at a virtual grand rounds seminar amongst all primate institutions with R25 primate trainees as well at the local Comparative Medicine Seminar hosted monthly by Yerkes.